330 CAUSES OF THE CRACKINGS OF TREES BY FROST. 



So again, Captain Anderson, of the Royal Engineers, 

 while employed on surveys connected with the North 

 American Boundary Commission, at the Lake of the 

 Woods, in Manitoba, thus states his experiences, while 

 sojourning there in a winter camp: 



" There were occasional days and nights of clear weather 

 and motionless atmosphere; on these occasions the thermo- 

 meter would show the greatest degree of cold, and in the 

 woods an audible evidence of its intensity was occasioned 

 by the freezing of the sap in the trunks and branches of 

 the trees, and the consequent bursting of the bark, with a 

 report like pistol shots. This chorus would sometimes continue 

 throughout the night, and the frequency and violence of the 

 reports would afford a good comparative measure of the 

 cold." * 



It will be observed that these authorities differ upon 

 the probable cause of this phenomenon, which may 

 arise from several causes, so that in the case of grow- 

 ing trees it may be that Captain Anderson's is the 

 correct one; whereas in perfectly dry timber, it is 

 probably simply due to the shrinking of the wood-- 

 loud cracks in floors, as we know, are common in 

 newly erected houses ; and in great cold, such as we 

 are now considering, there can be no doubt that the 

 frost increases the rigidity of the fibres of the timber, 

 so that when at length they do give way, they do so 

 with commensurate violence, accompanied with very 

 loud reports. But it is not wood alone, but all articles 

 of horn, bone, etc., also warp and fall to pieces just 

 as in very hot weather. 



The advent of the winter cold, we need hardly say, 



* Capt. S. Anderson, R.E., on the North American Boundary 

 Commission, in Vol. xlvi of the Journal of the Royal Geographical 

 Society for 1876, pp. 235, 236. 



